Sight Unseen takes a while to warm up, but it is worth the wait. The connections, especially the historical ones, seem a bit tenuous at the start but they are skilfully weaved together in the last half. There are still a few things that are too abrupt, like the father's departure, but on the whole the book is a good read.
It's also refeshing to see an historical investigation novel that actually takes seriously the methods and current concensus of historians. Very refeshing. It may be harder work to do the research and put forward a plausible hypothesis for the identity of Junius, but it gives the book a great deal more integrity.